Remove duplicated model declaration.

tests/models.py

@@ -184,10 +184,3 @@ class NullableOneToOneSource(RESTFrameworkModel):
 class BasicModelSerializer(serializers.ModelSerializer):
     class Meta:
         model = BasicModel
-
-
-# Models to test filters
-class FilterableItem(models.Model):
-    text = models.CharField(max_length=100)
-    decimal = models.DecimalField(max_digits=4, decimal_places=2)
-    date = models.DateField()